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Normal Vital Signs in Pregnancy

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Physiologic cardiovascular, respiratory, and thermoregulatory adaptations during pregnancy cause predictable changes in vital signs across gestation. The following trimester-specific reference ranges are derived from Green et al., Obstet Gynecol 2020.

Vital Sign Nonpregnant Adult 1st Trimester 2nd Trimester 3rd Trimester
Systolic Blood Pressure (mmHg) 90–120 94.8–137.6 95.6–136.4 101.6–143.5
Diastolic Blood Pressure (mmHg) 60–80 55.5–86.9 56.8–87.1 62.4–94.7
Heart Rate (beats per min) 60–100 63.1–105.2 67.4–112.5 64.5–113.8
Respiratory Rate (breaths per min) 12–20 8–24 8–24 8–24
Oxygen Saturation (SpO₂) (%) 95–100 94.3–99.4 92.9–99.3 93.4–98.5
Temperature (°C) 36.5–37.3 35.55–37.51 35.35–37.37 35.37–37.35
Temperature (°F) 97.8–99.1 95.99–99.52 95.63–99.27 95.67–99.23
Physiologic Changes Affecting Vital Signs
  • Blood Pressure: systemic vascular resistance decreases early → mild BP decrease in 1st–2nd trimester, returns to baseline in 3rd.
  • Heart Rate: increases 10–20 bpm from prepregnancy baseline due to ↑ stroke volume and ↑ cardiac output.
  • Respiratory Rate: unchanged, but tidal volume ↑ and minute ventilation ↑ by 30–50%.
  • Oxygen Saturation: usually maintained ≥95% despite physiologic respiratory alkalosis.
  • Temperature: progesterone increases basal temperature slightly early in pregnancy.

References

  1. Green LJ, et al. Gestation-Specific Vital Sign Reference Ranges in Pregnancy. Obstet Gynecol. 2020;135(3):653–664. PMID: 32028507